Polarographic electrode assembly



R. K. LADlscH ErAL 2,728,721

POLAROGRAPHIC ELECTRODE ASSEMBLY Filed May 29, 1953 Dec. 27, 1955 I" :'lll x INVENTORS Rolf Karl LadScL Jl Sanley L.Kz@$back ATTORNEYPoLARoGRAPmC ELEcTRoDE ASSEMBLY Rolf Karl Ladisch, Lansdowne, andStanley L. Knesbach, Philadelphia, Pa., assgnors to the United States ofAmerica as represented by the Secretary of the Army Application May 29,1953, serial No. 358,578 4 Claims. (Cl. 204-195) (Granted under Title35, U. S. Code (1952), sec. 266) The invention described herein ifpatented, may be manufactured and used by or for the Government forgovernmental purposes without the payment to us of any royalty thereon.

This invention relates to polarographic electrode assemblies of thedropping mercury type.

One of the objects of the present invention is to construct a droppingmercury electrode in such a way that the rate of flow of the mercury andthe drop size are maintained very nearly constant. Another object is tosimplify the construction. A further object is to construct theelectrode so that a single filling of the mercury reservoir will servefor about two weeks in polarographic testing. Another object is to makeit possible for the user to see what is happening inside the assembly. Aspecific object is to control drop times and the m2/3 t1/6 values with aprecision of r0.5 per cent.

Other objects will be apparent from the following description of thepreferred embodiment of the invention shown in the accompanying drawingsforming a part of this specilication.

In said drawings- Fig. l is a perspective view of the assembly;

Fig. 2 is a longitudinal section through the assembly; and

Fig. 3 is a cross section on line 3 3 of Fig. 2.

Referring particularly to the drawings, a tubular body 5, preferably ofglass, has a reduced lower end 6 in which a valve cock l is located. Acapillary 8 is connected to end 6 by means of Tygon tubing 9. Themercury drops (not shown) or" course fall from the lower end ofcapillary 8 into the test solution. At its upper end, tubular body 5merges with a reservoir 10 preferably cylindrical in form. Near its top,reservoir 10 has a filling hole or inlet 11 for introduction of themercury 12. Coaxial with the cylindrical reservoir 10 is a barometricinner reservoir 13 having a port 14 in its bottom wall 15. The innerreservoir 13 is also preferably cylindrical, and it may have a diameterof about one-half the diameter of the outer reservoir 10. ln thedrawings, the ratio of these diameters is about 4:7, which issatisfactory. Preferably inner reservoir 13 is of glass and it is fusedat its upper end to the top wall 16 of the outer reservoir 10 so as todepend therefrom and provide an annular chamber 17 of substantial volumebetween the inner and outer reservoirs. The bottom wall of reservoir 13lies above the bottom wall of reservoir 10 so that the mercury may flowfreely from chamber 1'! through port 14 into reservoir 13 and in thereverse direction. The upper wall 16 is constricted as at 18 to form atruste-conical neck, and a tube 19 is joined to the upper, smaller endof neck 18. A rubber or other collapsible bulb 2i? is fitted on theupper end of tube 19. Near the top of inner reservoir 13 a capillaryside arm 21 is attached, with its upper end communicating with theinterior of reservoir 13 and its lower end drawn to a point or tip 22. Acapillary passageway 23 extends the entire length of the side arm 21,and as shown, the lower pointed end 22 is located well above the bottomwall 15 of the inner reservoir 13. A wire or lead 24 is brought throughthe glass wall of reservoir 10 and through the wall of inner 2,728,721Patented Dec. 27, 1955 ICC reservoir 13 and is bent down to make a goodelectrical contact with the mercury 12 in the inner reservoir. It willbe understood that wire 24 is connected to a galvanometer (not shown)and the galvanometer is connected to a source of electric current suchas a battery (not shown), while the battery is connected to apolarographic half cell, as in the usualpolarographic set-up. See Fig. 5of the R. K. Ladisch pending application Serial No. 220,325, VfiledApril 10, 1951, now Patent No. 2,708,657,

issued May 17, 1955, for an illustration of the complete circuit.

To operate the described electrode, valve cock 7 is closed and mercuryof the purity demanded forl polarographic use is introduced .throughinlet 11 to a height corresponding approximately to half the length of.Athe capillary sidearm 21. Then the rubber bulb 20 is squeezed andreleased. This forces part of the air (which-was above the surface ofthe mercury confined in inner reservoir 13 out through the capillarysidearm; this airv escapes in bubbles to the surface of the mercury andenters annular chamber 17, which is open to the'atmosphere. Asthe air inthe upper part of inner reservoir 13 is consequently of reducedpressure, the mercury level will rise in inner reservoir 13 to reach astate of equilibrium or a balancing of the pressures. The level in theouter reservoir comes into balance at a height h, which is the height ofthe lower tip 22 of the capillary sidearm; lthis tip acts as` a valve,permitting air to ow from the outer reservoir into the inner reservoirthrough the capillary sidearm until the rise in the mercury level in theouter reservoir seals off the tip. The described electrode may then beput in service by merely opening the valve cock 7, whereupon drops ofmercury at a known rate will proceed to fall one by one into the testsolution. Then readings are taken on the galvanometer in accordance withthe well-known polarographic technique. During the course of thisanalysis, mercury is steadily lost to the electrode by the drops fallingfrom capillary 8, but the level of the mercury in the outer reservoir ismaintained at height h until, after many analyses, the mercury in theinner reservoir 13 has fallen close to the level of tip 22. Then themercury supply may be replenished by introducing additional mercurythrough inlet 11, and analyses by and polarographic technique mayproceed.

The constancy of the mercury level in the described assembly was checkedduring a series of test runs using a cathetometer. In no case did thedeviation exceed 0.5 mm., according to our observation. The drop time tas well as the mass flow m as determined in a one-tenth normal KClsolution, held by a thermostat to 25 C: 0.05", remained constant within20.5 percent. Some typical data, selected at random from one daysoperation of the described electrode assembly, are reproduced in thefollowing table:

Table I.-Drop time and mass flow of mercury obtained from 3 capillariesin combination with new electrode assembly.

[Pio N KCI solution, 25;l;0.05 C. Room temperature not controlled] Fromthese data the radii of the capillaries were calculated (Koltho andLingane, Polarography, vol. I,

p. 80, Interscience Pub., New York, 1952). They were The valuescalculated by this formula for the capillaries 1, 2 and 3 of the tablewere 3.24, 5.18 and 6.26 seconds respectively, which is in goodagreement with the drop times actually measured.

` The electrode assembly described above and illustrated in the drawingsis simple, convenient to manipulate, and extremely reliable. With agiven capillary it maintains a constant pressure due to head h overaperiod of several weeks oncontinuous operation with routine analyses.

What we claim is:

1. A dropping mercury electrode assembly comprising an outer lreservoiropen to the atmosphere and having suicient volume to hold a substantialsupply of mercury, an inner reservoir wholly enclosed by and spaced fromthe outer reservoir, said inner reservoir having a bottom wall with aport providing a passage for free How of mercury between the reservoirs,a suction member, the inner reservoir being sealed off from theatmosphere and having means connecting itwith the suction member, acapillary sidearm connected to the upper part of the inner reservoir andextending down in the space between theV inner and outer reservoirs, avalved tube connected to the bottom of the outer reservoir, a capillary,and means connecting the capillary and valved tube so that mercury owsthrough the valved tube to the capillary and is discharged in drops fromthe lower end of the capillary.

2. The invention defined in claim l, wherein the suction member is acollapsible rubber bulb, and the outer reservoir is entirely sealed offfrom the atmosphere except for a lling opening near its upper end.

3. A dropping mercury electrode assembly comprising an outer glassreservoir having a lling port for mercury and having a tubular extensionextending downwardly from its lower end, a valve cock in said tubularextension for controlling llow of mercury, a capillary coupled to thelower end of the tubular extension to discharge the mercury in a seriesof drops for polarographic analysis, an innerglass reservoir fused atits upper end to the upper end of the outer reservoir and receiving itssole support fromits connection with the outer reservoir, there being asubstantial space between the walls of the inner and outer reservoirsexcept at the aforesaid fused joint, the bottom walll of the innerreservoir having a passage for free flow of mercury, a capillary sidearmconnected at its upper end to the interior of the inner reservoir andextending down alongside the outer wall of the inner reservoir with itslower end reduced to a ne tip which is spaced well below the medialhorizontal plane of the inner reservoir, and a suction means connectedwith the upper part of the inner reservoir.

4. The invention defined in claim 3, wherein the suction member is acollapsible rubber bulb, and the outer reservoir has an open port nearits upper end for introduction and replenishment of the mercury supply.

"Analytical Chemistry, vol. 22, No. 9 (September 1950), pages 1213 and1214.

1. A DROPPING MERCURY ELECTRODE ASSEMBLY COMPRISING AN OUTER RESERVOIROPEN TO THE ATMOSPHERE AND HAVING SUFFICIENT VOLUME TO HOLD ASUBSTANTIAL SUPPLY OF MERCURY. AN INNER RESERVOIR WHOLLY ENCLOSED BY ANDSPACED FROM THE OUTER RESERVOIR, SAID INNER RESERVOIR HAVING A BOTTOMWALL WITH A PORT PROVIDING A PASSAGE FOR FREE FLOW OF MERCURY BETWEENTHE RESERVOIRS, A SUCTION MEMBER, THE INNER RESERVOIR BEING SEALED OFFFROM THE ATMOSPHERE AND HAVING MEANS CONNECTING IT WITH THE SUCTIONMEMBER, A CAPILLARY SIDEARM CONNECTED TO THE UPPER PART OF THE INNERRESERVOIR AND EXTENDING DOWN IN THE SPACE BETWEEN THE INNER AND OUTERRESERVOIRS, A VALVED TUBE CONNECTED TO THE BOTTOM OF THE OUTERRESERVOIR, A CAPILLARY, AND MEANS CONNECTING THE CAPILLARY AND VALVEDTUBE SO THAT MERCURY